Though I've long been obsessed with American culture of the late 1970s and the very early 1980s – in terms of cinematic mis-en-scene, particularly costume and production design – I've never seen a film that addressed it directly. Mike Mills' new indie feature, 20th Century Women is set in Santa Barbara, California in 1979. Mills takes this historical moment and unpacks it with loving attention to the behaviours, attitudes, politics and cultural markers of the time.

While the film ostensibly tells the story of a single mother Dorothea Fields (a glorious, radiant, wry chain-smoking Annette Benning) and her teenage son Jamie (Lucas Jade Zumann) as they negotiate his growing independence, it's also a loose portrait of women in his life – these are the 20th century women of the title – his childhood crush and object of affection (Elle Fanning) and their housemate, a twenty-something budding artist going through a personal crisis (Greta Gerwig) weathering it in the safety of their rambling mansion, a grand old building being restored by a middle-aged hippy mechanic (Billy Crudup).

Overlook the slightly contrived set up; it doesn't make much sense. Mills is not a director all that interested in plot but what it lacks in narrative momentum or sense of urgency it more than compensates with a loose, open-ended energy and a commitment to exploring age, especially middle age, and the internal and external forces that shape us. He has an eye for dramatic images – a car sitting in a parking lot in flames, Jamie elegantly and perilously skateboarding down steep Santa Barbara boulevards – that render the ordinary poetic.

Teenage Jamie likes to repeat that Dorothea was born in the Depression, a shorthand way of describing their difference in age as well the changed world he is coming of age in. When the motley crew sit down to watch President Jimmy Carter's speech on the 'Crisis of Confidence' about the rise of materialism in America Dorothea is the only one who agrees with its sentiments. But in many other respects she's a woman of her time: taking wealth creation into her own hands with a stocks portfolio, a professional job, and, in one very funny scene, cutting a dinner party short when the conversation steered by the younger women veers towards the subject of menstruation.

While Dorothea worries about the kind of man Jamie will grow to be, Jamie concerns himself with what he perceives as Dorothea's loneliness. But is she lonely? I wasn't so certain. Jamie's worry exposes the difficulty of their relationship, the mutual love and worry that underpins it. I loved 20th Century Women's tenderness and claim it makes for the importance of sharing the things that excite us – music, books, ideas – while maintaining that the very things that shape us also set us apart. And then there are the shirts. In its loving homage to the late 1970s it rifles through the wardrobes from the era and pulls out not one or two but too many good shirts to mention.